Dynamic Heat Dissipation Model of Distributed Parameters for Oil-Directed and Air-Forced Traction Transformers and Its Experimental Validation

Abstract

A traction transformer with narrow oil channels is usually cooled with the ODAF or “Oil Directed Air Forced” method, where its temperature greatly depends on the Joule heat of windings, the conjugate heat transfer in the transformer, and the secondary heat release via oil cooler, together with the oil flowrate generated by oil pump. Neither the thermal–electric analogy nor the CFD simulation approach is qualified to predict the temporal and spatial temperature variations in this type of transformer. In the current work, the distributed parameter models are built for traction transformers and oil coolers with the assumption of a one-dimensional temperature field in the oil flow direction, respectively. Then, the two models are combined with the lumped parameter ones of oil pumps and pipes via the flow rate, temperature and pressure continuities at their interfaces, resulting in the derivation of the dynamic heat dissipation model of oil-directed and air-forced traction transformers. Additionally, an efficient algorithm is proposed for its numerical solution, and the temperature rise experiment is performed for model validation. Finally, the fundamental of dynamic heat dissipation in traction transformers is investigated with the current numerical model and the effects of ambient temperature are studied.

Proof of the Concept of Detailed Dynamic Thermal-Hydraulic Network Model of Liquid Immersed Power Transformers

“…Supposing the value of k pp is known (its determination is described in the further text), the thermal resistance R pp T can be calculated, according to Equation (11), for each of the six pipe sections and each of the three heater case sections, using corresponding lengths and diameters. The heat transferred to these sections, with inlet temperature ϑ in and outlet temperature ϑ out , is calculated by dividing the average water ((ϑ in + ϑ out )/2) minus the ambient temperature difference by R pp T of that pipe section.…”

“…Some researchers are trying to create hybrid models by combining the lumped models of some transformer parts with the distributed parameter models for the other. This possibility is explored and experimentally validated for the special type of traction transformer [11].…”

Research on the influence of extreme high temperature weather on transformers and their cooling

“…In the design of transformer operating in discontinuous current mode： (1)Peak current measurement at one timeI P 。Single-tube converters supply power to the converters by DC, and the power obtained by the single-tube converters is determined by the DC components (or average values) of voltage and current. If the input voltage is DC, and the input current is intermittent cogging current, the output power is…”

“…The heat dissipation of oil-immersed transformer is mainly manifested in the following three forms: thermal convection, thermal conduction and thermal radiation. The specific heat dissipation process is as follows：The heat generated by transformer coil and iron core is transferred to the surface through heat conduction, then cooled by transformer oil, transferred to the internal surface of oil tank or radiator through thermal convection, and released to the atmosphere through thermal convection and thermal radiation [8]. The cooling principle of oil-immersed self-cooling transformer is that the coil and iron core will release heat, which will cause the temperature of insulating oil at the bottom of transformer to increase, which will cause the density of insulating oil at the bottom to decrease, thus making the oil move upward [9].…”

“…Transformer is one of the important industrial equipment in power engineering and plays an important role in ensuring the normal operation of power engineering. In order to ensure the safe and stable operation of transformer, efficient heat dissipation is very important [1]. When the transformer works, iron and copper may produce corresponding losses, while when electric energy is lost, it will emit a lot of heat and gradually raise the temperature of the transformer, thus affecting its efficiency [2].…”